Automotive vehicles have been produced with computer-controlled brake systems that modulate brake force during stops to provide anti-lock brake (ABS) control and/or that modulate brake force during vehicle acceleration to provide positive acceleration traction control (TCS). Recently, more comprehensive computer-based vehicle brake control systems have been developed that provide additional chassis control under braking or positive acceleration conditions. Such systems are described, e.g., in U.S. Pat. Nos. 5,720,533 and 5,746,486, both entitled "Brake Control System" and assigned to the assignee of this invention. These systems seek to control, among other parameters, the yaw rate of the vehicle.
The computer in the chassis control systems described in these patents uses signals from a variety of sensors such as wheel speed sensors, steering wheel angle sensor, brake switch sensor, brake pedal extended travel sensor, master brake cylinder pressure sensor, yaw rate sensor and a lateral accelerometer. For further development of such control systems, it is desirable and/or necessary to provide algorithms or computer-controlled processes for eliminating some of such sensors or for detecting faults in their operation.
For example, a process has been developed that permits vehicle yaw control based on an estimated yaw rate rather than the output of a yaw rate sensor. This practice is described in U.S. Ser. No. 09/080,372, entitled "Vehicle Yaw Control Based on Yaw Rate Estimate" and assigned to the assignee of this invention. While this yaw rate estimate practice can eliminate the use of a yaw rate sensor, it does use the output of a brake pedal travel sensor to measure the extent of driver braking. Such a sensor is expensive compared to a marginal increase in on-board computer processing capacity and, furthermore, the sensor is subject to failure.
Accordingly, it is an object of this invention to provide a process for determining whether a brake pedal travel sensor is faulty or for eliminating the need for input from such a sensor, especially in making computer-based estimates of vehicle yaw rate.